Cardiovascular disease is a leading cause of death around the world. Its prevalence is growing with congestive heart failure (CHF) representing the biggest proportion. Current treatment for end-stage CHF is transplantation, but of 40,000 patients in the US under age 65, less than 3,000 will receive transplants in any year. Most patients die while waiting for a transplant. Ventricular assist devices can help some patients as a bridge to transplantation. Implantable artificial hearts will help others, and serve as a permanent solution for patients with rejection problems. For these patients to have a near-normal life requires a compact, high energy density storage system so they can move about freely. Phase I of this SBIR project demonstrated the efficacy of direct methanol fuel cells (DMFCs) in this role. DMFCs consume high energy density methanol solutions (600 Wh/L for a 10 percent solution) at temperatures slightly above ambient and deliver electrical power. DMFC stacks were demonstrated to start at room temperature, heat to operating temperature, and reliably supply electricity with a power density of 53 mW/cm_, requiring only a small fan to supply air and a small pump to deliver fuel as its balance of plant. The stack used to collect this data was fabricated from lightweight materials using standard industrial processes to insure that the final power supply resulting from this project will be manufacturable. PROPOSED COMMERCIAL APPLICATION: Nearly 500,000 people die from congestive heart failure in the US each year, with the total exceeding 3,000,000 around the world. At least half of them could benefit from a TAH or a VAD. These devices are currently in advanced stages of testing with secondary batteries as their only power supply. As they come into wider use higher energy density power supplies will be needed to give these patients a more normal life. This is the market that the proposed power supply addresses.